go to thetford site www.thetford-europe.com
I'm currently in La Fleche France on caravan site Camping municipal route D'or site very nice
the edge of the town and entrance can can be seen on google maps street level, or satellite view.
Click service, click arrow on service information, click toilets then cassette toilets
Scroll and click on 250 then select repair instructions and any others you want in turn, it sounds like a fuse has blown.
Good luck sorry can't be of more help
Bob & 'er indoors' UK/Fr.
July 2014
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix caravans/motorhomes.